People with atrial fibrillation (AF) have irregular heart beats and have a tendency to form blood clots in the upper chambers (atria) of their hearts. These clots can then travel to the brain, block vessels and cause a stroke. One way of reducing the risk of this occurring is to give drugs that limit the bloods ability to create clots. Two commonly used options are anticoagulants that inhibit the clotting process (e.g. warfarin), and drugs such as aspirin that make blood platelets less likely to bind together and trigger a clot.

In standard medical practice, anticoagulants are often given to people with AF who are at high risk of strokes, while anti-platelet treatments are offered to people at lower risk.

A team of Cochrane Researchers set out to compare the relative benefits of these two treatments. After searching the medical literature, they drew on data found in eight trials that together involved a total of 9598 people who had AF but had not suffered stokes so far.

The results showed that anticoagulants were more successful than anti-platelet therapies at reducing stroke. They reduced the risk of a stroke in people with AF by about 33% compared with anti-platelet therapies. The anti-platelet therapies did, however, still have an effect, reducing the risk by 20% when compared to people who were given no treatment (controls).

Adjusted-dose warfarin offers larger, more predictable reductions in stroke for AF patients who can receive it, says lead researcher Maria Aguilar, who works in the department of Neurology at the Mayo Clinic Scottsdale, Arizona, USA.

While it is clear that both drugs can bring benefit, it is unclear at what point a person should start to take them.

The threshold of benefit that would warrant anticoagulation remains controversial and depends on patient preferences and availability of optimal anticoagulation monitoring, says Aguilar.